1. Field of the Invention
An embodiment of the present invention relates to an optical scanner having an improved driving angle and a laser image projector using the same, and more particularly, to an optical scanner including a micro-mirror having an increased improved angle by using a micro-electro-mechanical system (MEMS) technique and a laser image projector using the same.
2. Description of the Related Art
A MEMS micro-actuator structure using an electrostatic effect of a comb-typed electrode is used as an optical scanner for deflecting a laser beam in a projection TV. FIG. 1 is a perspective view illustrating a structure of a conventional optical scanner. As shown in FIG. 1, the conventional optical scanner includes a substrate 5, a mirror unit 1 suspended over the substrate 5, a supporter 6 supporting both ends of the mirror unit 1, a torsion spring 2 connected between the mirror unit 1 and the supporter 6 and supporting a seesaw movement of the mirror unit 1, a plurality of movable comb electrodes 3 vertically formed on both sides of the mirror unit 1, and a plurality of static comb electrodes 4 vertically formed on the substrate 5 in such a way that the static comb electrodes alternate with the movable comb electrodes.
FIG. 2 is a sectional view illustrating an operation of the conventional optical scanner shown in FIG. 1. Referring to FIG. 2, a predetermined voltage is applied to movable comb electrodes 3a and 3b formed on both sides of the mirror unit 1, and a positive voltage and a negative voltage are respectively applied to static comb electrodes 4a and 4b corresponding to the movable comb electrodes 3a and 3b. For example, a voltage V1 is applied to both the left movable comb electrode 3a and the right movable comb electrode 3b, a voltage V is applied to the left static comb electrode 4a and a voltage −V is applied to a right static comb electrode 4b. Then, a voltage difference between the left movable comb electrode 3a and the left static comb electrode 4a becomes different from a voltage difference between the right movable comb electrode 3b and the right static comb electrode 4b, and thereby the mirror unit 1 is inclined to one side by static electrical force, as shown in FIG. 2. In the meantime, the mirror unit 1 returns to its original place by restoration force of the torsion spring 2. Therefore, the mirror unit 1 can be periodically moved by a predetermined driving angle and a predetermined driving speed (i.e., driving frequency) by properly adjusting the voltage applied to the movable comb electrodes 3.
In the meantime, an optical scanner should scan a laser beam at very rapid speed in order to embody an image on a screen of a laser image projector. In general, a mirror unit should have small mass in order to increase its driving frequency. However, if the size of mirror unit 1 is reduced in order to decrease its mass, then a diameter of a laser beam reflected by the mirror unit 1 is also decreased. However, if the diameter of the laser beam reflected by the mirror unit 1 is decreased, then the laser beam is spread on the screen. This phenomenon deteriorates resolution of an image displayed on the screen.
Therefore, in order to increase resolution of an image, the size of the mirror unit 1 should be increased so that a laser beam having a large diameter can be reflected by the mirror unit 1, or a driving angle of the mirror unit 1 should be increased. However, if the size of the mirror unit 1 is increased, then a driving speed of the optical scanner is decreased due to the mass increase of the mirror unit 1. Also, there is a limitation in increasing a driving angle of the mirror unit 1. This is because if the movable comb electrodes 3 completely enter between the static comb electrodes 4, then the driving force is not generated anymore and thereby the mirror unit 1 does not rotate anymore. In this case, in order to increase the driving angle of the mirror unit 1, the height of the movable comb electrodes 3 and the static comb electrodes 4 should be increased so that an angle at which the movable comb electrode 3 and the static comb electrode 4 completely overlap each other is increased. However, this increase in thickness of the mirror unit 1 for increased the driving angle also causes an increase in the mass of the mirror unit 1.